The limited published research on pollination
ecology within the Iridaceae has tended to emphasize genera with
meranthia of gullet flowers such as Iris, Moraea,
and Gynandriris (Faegri & van der Pijl, 1979). The
pollination ecology of Lapeirousia, however, is far closer
to what has been described in the southern African genus Nivenia
(Goldblatt & Bernhardt, 1990). In Nivenia floral tubes
are not occluded and the stamens and styles are prominantly displayed.
The flowers are pollinated by long-tongued bees and nemestrinid
flies in the genus Prosoeca. Access to the nectar secreting
tube is direct and the insect head and thorax contact the anthers
and stigma while the insect hovers or clings to the tepals.

The disparity between the length of
perianth tube in subgenus Lapeirousia and the shorter length
of the mouth parts of the primary pollinators is quite easy to
explain. Records of nectar secretion show that species in subgenus
Lapeirousia secrete copious amounts of fluid for insect-pollinated
flowers, and it is most unlikely that dominant pollinators are
ever forced to extend their mouth parts to the base of the tube
unless all the nectar has been removed by earlier foragers. More
important, Darwin (1862) hypothesized that successful pollination
of spurred orchids occurred when orchids evolved floral spurs
slightly longer than the tongues of their pollinators, forcing
the insect to ram its head down the floral throat, ensuring contact
between the insect's head and the orchid's column. This has since
been shown experimentally by Nilsson (1988). As in the nectariferous
orchids, species in subgenus Lapeirousia "oblige"
their pollinators to make contact with the anthers and stigmatic
surfaces of the style branches of the flowers that block or at
least encircle the entrance to the floral tube.

Some members of subgenus Lapeirousia
appear to be self-compatible. Spatial isolation between anthers
and stigmas is not always well expressed in subgenus Lapeirousia
and protandry is weakly developed. Four Lapeirousia species
show successful fruit and seed production in the absence of pollinators.
This is most likely the result of mechanical autogamy. (We consider
the alternative possibility that apomixis takes place most unlikely:
the phenomenon is unknown in Iridaceae.) Three of the four species
that show self-pollination start flowering during the southern
African winter when rain and low temperatures may restrict pollinator
activity. Mechanical autogamy by contact between the stigmatic
surfaces and the pollen (or apomixis) then becomes a fail-safe
mechanism in the absence of dependable pollinators. This has also
been described in the late winter-early spring flowering herbs
of North America (Schemske et al., 1978) and some terrestrial
orchids of southern Australia (Dafni & Bernhardt, 1989).

There are two major differences between
floral mechanisms in Nivenia versus Lapeirousia.
First, fly-pollination in Nivenia appears to be restricted
to nemestrinids. In some Lapeirousia species pollination
may be dependent on the long-tongued tabanid, Philoliche gulosa.
Second, and more important, analysis of floral presentation and
observation of floral foragers emphasize that pollination systems
in southern African species of subgenus Lapeirousia can
be subdivided into a minimum of three syndromes, or perhaps four
if the sphinx moth syndrome is regarded as separate from the generalist
system that otherwise prevails in those species with the L.
divaricata-type flower.

Pollination by nectar foraging flies
has been treated as a relatively common but unspecialized syndrome
in which many fly taxa visit the same flower, and the dispersal
of pollen may be shared with co-foraging bees and butterflies
(Grant & Grant, 1965; Barth, 1985). We may compare the more
classical treatment of myophily with our results. Fly-pollination
in Lapeirousia has evolved into such a specialized syndrome
that two different modes of floral presentation appear to attract
and depend on two different sets of fly genera. Species with the
L. silenoides type of flower appear to depend exclusively
on two species of flies in one genus, Prosoeca. We also
note that plants with the L. silenoides-type flower appear
to be restricted to the west coast and adjacent near interior
of southern Africa. The species exhibiting the L. fabricii-type
of presentation frequently have marginally longer tubes than species
that have the L. silenoides-type flower and seem to be
pollinated exclusively by Moegistorhynchus longirostris
and Philoliche gulosa. Plant species with this flower type
occur widely across southern Africa, although they appear to be
most frequent in the southwest and west of the subcontinent. Among
the species with this type of flower, L. anceps stands
out in its remarkable range of perianth tube lengths, 20-76 mm.
The pattern suggests that only populations in the west and north
of its range with tubes 45-76 mm long are pollinated by M.
longirostris, because nectar is accessible to only this fly,
given the length of its proboscis. Populations with shorter tubes,
as little as 20-30 mm in the south of its range, cannot be pollinated
by this fly species, which does not occur in this part of the range
of L. anceps. The pollinator(s) for these short-tubed plants
must be some other, presumably long-tongued fly, possibly Philoliche
gulosa which does occur here and has a proboscis 20-33 mm
long. Evidently, tube length is extremely labile and may respond
rapidly to selection by pollinators.

Despite the segregation of Lapeirousia
species into three pollination guilds, the majority of species
in this subgenus secrete sucrose-rich/sucrose-dominant nectar
regardless of the major pollinators. This adds a new dimension
to the analytic work and categorization of nectar by Baker &
Baker (1983, 1990). In their earlier treatments of myophily the
Bakers found that fly-pollinated flowers tended to be weak in
sucrose, like the flowers pollinated by short-tongued bees. However,
when the Bakers analyzed fly flowers they concentrated on taxa
pollinated by short-tongued flies, such as the Muscidae, Syrphidae,
and Phoridae. It now appears that just as flowers pollinated by
long-tongued bees are usually rich in sucrose (Baker & Baker,
1983, 1990), flowers pollinated by long-tongued flies are also
sucrose producers. Perhaps pollination by large-bodied physically
active insects that maintain wing movement while feeding (e.g.,
nemestrinids, Philoliche, sphinx moths and some anthophorids
(Goldblatt & Bernhardt, 1990) requires an emphasis on sucrose
instead of hexose rewards that is independent of insect order.

Although certain Lapeirousia
species may be pollinated by only one or two fly species, the
degree of dependency in this insect-flower relationship is not
shared to the same degree by the flies. As in so many proposed
cases of co-adaptation, the Lapeirousia flowers appear
to have become modified for pollination by specific flies to a
greater extent than flies have become modified for Lapeirousia
flowers. The evidence for this unequal relationship is presented
in the polytrophic foraging behavior of flies at field sites and
confirmed by the results of pollen load analyses. It is more likely
that the Lapeirousia species with L. silenoides-type
and L. fabricii-type flowers belong to broader guilds,
encouraging the partitioning of long-tongued fly pollination into
more than one syndrome in the southern African flora. Observations
on flowers in other genera and families visited by long-tongued
flies, e.g., Babiana and Hesperantha (Iridaceae),
Pelargonium (Geraniaceae), suggest that floral presentation
for pollination by Prosoeca species or by Moegistorhynchus
and Philoliche shows a high degree of convergence in such
floral characters as color patterns and tube or spur length. The
types of floral presentation in southern African plants
pollinated by different fly genera and species may ultimately
prove to be as diverse as, yet distinct from, pollination guilds in
other parts of the world, such as members of the neotropical flora
that are pollinated by straight-billed hummingbirds versus those
plants taxa pollinated by hermit hummingbirds with curved bills
(Feinsinger & Colwell, 1978; Feinsinger et al., 1985).

Pollen-load analysis of the bee-pollinated
members of the Lapeirousia divaricata group suggests community
dynamics typical of flowers pollinated by long-tongued bees in
other parts of the world. These anthophorids and long-tongued
bees in the Apidae (e.g., Bombus, Euglossa) often
show foraging strategies in which individual bees balance visits
to nectarless flowers [e.g., Dianella (Phormiaceae), Echeandia
(Anthericaceae), Schrankia (Fabaceae), Acacia (Fabaceae),
Hibbertia (Dilleniaceae) that offer copious pollen with
visits to plants that produce copious nectar, but from which pollen
is not collected actively (Bernhardt, 1989, 1990; Bernhardt &
Montalvo, 1979; Bernhardt, 1995). The presence of the pollen
of nectarless Cyanella and Hermannia on female anthophorids
collected on flowers of the L. divaricata-type suggests
that community pollination by long-tongued bees in southern Africa
may not be significantly different from those syndromes cited
above for the floras of Central America and southern Australia,
and the woodlands and prairies of North America (Schemske et al.,
1978).

Members of subgenus Lapeirousia
now join an expanding list of plant taxa in which segregated pollen
flow is due in part to ethological isolation (Grant, 1994). In
subgenus Lapeirousia ethological isolation (sensu Grant,
1994) appears to be based on two factors. First, as in Aquilegia
(Ranunculaceae), different pollinators may be restricted to different
plant taxa as a partial consequence of mechanical isolation (Grant,
1971), as bees and moths are probably unable to forage successfully
on the flowers of Lapeirousia species in which tube length
far exceeds tongue length. Second, ethological isolation must
also be based in part on flower constancy as differing modes of
floral presentation, featuring diverse color patterns and scent
production, produce different responses in the foraging behavior
of local pollinators that are polytrophic and/or polylectic. That
is, flies and bees are not expected to respond to the same forms
of floral advertisement due to their different visual and olfactory
senses (Barth, 1985).

Observations of interspecific hybridization
in sympatric and co-blooming populations of Lapeirousia fabricii
and L. jacquinii, and of L. silenoides and L.
verecunda respectively, indicate that when members of the
different pollination guilds are sympatric, ethological mechanisms
are sometimes insufficient to prevent interspecific pollination,
as evidenced by the recent discovery of scattered hybrids between
members of each of the above pairs. In fact, species belonging
to different guilds seldom co-occur and when they do they usually
flower at different times. These observations suggest that floral
divergence is not a result of selection for prepollination isolating
mechanisms.

Postpollination isolating mechanisms
may operate in Lapeirousia jacquinii and L. violacea.
These species belong to the same guild and have been seen to be
visited by the same fly individuals. Despite this, no F1 hybrids
have been found after three years of fieldwork and it seems likely
that biochemical recognition and rejection of interspecific pollens
may be a more important form of interspecific isolation within
some Lapeirousia species belonging to the same pollination
guild. However, in other instances interspecific pollen recognition
may offer incomplete isolation, as L. jacquinii and L.
pyramidalis subsp. regalis have the same mode of floral
presentation and hybrids between the two have been recorded at
one site (Goldblatt & Manning, unpublished).

Information on pollination systems in
subgenus Lapeirousia may now be combined with a cladistic
analysis to help determine the evolution of pollination syndromes,
extensively discussed by Goldblatt & Manning (in mss). The
picture that emerges from that study Figure 5 indicates most
strongly that the dependence of a Lapeirousia species on
a particular guild of long-tongued pollinators has originated
several times. While it is true that some sister species (e.g.,
L. dolomitica and L. violacea or L. divaricata
and L. spinosa) share the same pollination syndrome, this
sharing appears to be an exception within the current phylogenetic
tree. From the combined data we conclude that floral evolution
in subgenus Lapeirousia is extremely labile and probably
reflects a rapid response to the relative diversity of potential
vectors within a given geographic area.

It is possible to predict with some
degree of confidence the ancestral mode of pollination within
subgenus Lapeirousia. We know that in the outgroup, subgenus
Paniculata, the majority of species bear relatively short-tubed
flowers with pollination types most similar to the L. divaricata-type
in subgenus Lapeirousia. Goldblatt (1990) reported that
two species, L. erythrantha (Klatt) Bak. and L. avasmontana
Dinter (both tropical members of subgenus Paniculata),
are actively visited by bees, wasps, and diurnal Lepidoptera,
and L. sandersonii Bak. of the subgenus is visited predominantly
by diurnal Lepidoptera (Manning, unpublished). This is consistent
with our observations here (Table 2) for L. azurea (Eckl.
ex Bak.) Goldblatt, L. fastigiata (Lam.) Ker-Gawl., and
L. neglecta Goldblatt & Manning, and Scott Elliot's
(1891) report for L. corymbosa (all subgenus Paniculata),
also most commonly visited by bees. Therefore, short-tubed and
funnel-shaped flowers dependent on Hymenoptera and Lepidoptera
may be basal to subgenus Lapeirousia, and it seems far
more parsimonious to infer that flowers with long perianth tubes
and associated nectar guides are ultimately derived from short-tubed
flowers with simple nectar guides. In light of this, the terminal
position of the species pair, L. divaricata-L. spinosa,
primarily pollinated by bees, and nested within a clade of long-tongued
fly-pollinated taxa, evidently represents a reversal to an ancestral
pollination strategy. This emphasizes the extreme degree of adaptive
radiation exhibited within subgenus Lapeirousia and the
impact of pollinators on floral morphology and biochemistry.